Apparatus for heating fluids



Nov. 21, 1950 D. H. GREENE APPARATUS FOR HEATING FLUIDS Filed April 29, 1947 GAS OUT UAW H. GRE ENE Patented Nov. 21, 1950 UNITED STATES PATENT OFFICE APPARATUS FOR HEATING FLUIDS David; H. Greene, Los Angeles, Calif., assignor to Danciger Oil & Refining Company, Fort Worth,

Tex., a corporation of Texas Application. April 29, 1947, Serial'No. 744,563

Claims. 1

This-invention relates toan improved apparatus ior heating. fluids, particularly gases, to high temperatures.

As is known, it is possible to effectivel heat gases to temperatures-of .1800" F. and below by installing a metallic tube or series of tubes in a suitably heated ifurnace. For operation in. such a temperature range, steels of various analyses and certain non-ferrous alloy tubes have been employed heretofore. However, when gases are to be heated to elevated temperatures above 1800 F; or 2900' :such alloy tubes are not suitable. Under such very high temperature operation stresses are imposed. on the tubes inducing distortion: and with even most expensive heat resistant alloy tubing the alloys soon become soft and lose their rigidity. The high initial cost of the alloy tubes coupled with constant-necessary replacement with concomitant loss of operating time due to shut down imposes serious economic restrictions on their use.

As is known, at :the present time refractory tubing is available which will withstand. temperatures of the .order of 2000 F; and :above. This type of tubemay be fabricatedfrom readily available refractories suchas'alumina, zirconia,,beryllium oxide and silicon carbide. These refractories also may be molded or otherwise formed into units such as return bends, Us and the like. It is thus possible by associating the tubes with returnbends or Us to construct a continuous coil of any desired length which coil may be disposed either horizontally or vertically in a furnace. Likewise, manifoldscan be .iabricated from. these refractories so that, if desired, .two or more tubes can be disposed in thecoil in parallel.

It is apparent that a continuous coil of the described type comprising a plurality of tube units and return bends or equivalent connecting elements necessarily involves a series of joints between the several elements. While-a continuous tube of this type presents the advantage of marked utility at high temperatures, in the past .it-had been. found practically impossible to con.- struct sume-continuous coil which would be gastight over an commercially practical period of operation. The presentinvention provides a solu- .tion for this problem of producing a gas-tight continuous refractory tubing for operation at highly elevated temperatures.

In 'OIdGIZTtOGHfiblE amore. ready comprehension of the invention typical, though not exclusive, physical embodiments are shown i-n-the accompanying drawing in-which:

. Fig. 1 is asectionalrelevation of l a furnace con- 2 taininga continuous-refractory coil according to the invention.

Fig; 2 is an enlarged detail of a section of the refractory coil shownin Fig. 1, and

Fig. 3 isa diagrammatic plan viewillustrating an alternative disposition of the coil elements.

The rationale oftheinvention as well as the advantages to bederived from its use can be more readily appreciated from a consideration of the mechanism of the failures which. have been encountered heretofore. In the past, when refractory coils of the type discussed have been employed for heating fluids at high temperatures difiiculties arose due to the fact thatat the high temperatures involved both linear and cubical expansions are relatively large. As will be appreciated, in this type of construction, the tubes and return bands, due to thermal expansion, assume a position at high temperatures quite different from that prevailing at low temperatures. As a practical matter, for efiicient operation, the continuous coil should be gas-tight when cold and yet remain gas-tight under-operating conditions at temperatures above 2000 F. It has been found by experience that joints that are gas-tight at lower vtemperaturesmay not prevent the leak age of the. gas at higher temperatures clue to the displacementof the elements of the continuous coil with consequent .fracture of the joints and tubes.

The salient object of the present invention therefore is to produce a continuous coil made up of associated tubesand return bends or equivalent interconnecting members in which a novel -.-type of floating movement is permited between the elements thus obviating or compensating for'the mechanical stresses whichhave heretofore caused leakage at the jointsand, in many instances, fracture of the tubes themselves.

It has been ascertained that this desirable result may be achieved by establishing floating curvilinear contact surfaces between the tubes and certain of the interconnecting elements, such .as returnbends, manifolds, .Ls and the like, and

after, insures the desired rigidity in the coil structure as a whole while rendering it gas-tight,

at both high and low temperatures, for protracted operative periods.

As shown in the drawing the improved continuous coil may be embodied in a suitable furnace I, having the side walls 2, roof 3 with associated stack 3 and the floor 4. The coil is constructed of material such as silicon carbide or equivalent highly refractory compounds. The coil itself is comprised of the fabricated standard interchangeable and readily replaceable tube sections of suitable length which are joined together by the upper return bends G at the joints 8 and lower return bends 1 at the joints 9. Ohviously, the coil may be made up of any desired number ofi tube units and associated return bends. The coil may be connected to units exterior of the furnace in any suitable manner. In one example the tubes l0 and I l extend exteriorly of the furnace and may be connected to the coil by means of the Us !2 and I3 respectively at the joints I 4 and I5. The tube It, as shown, is provided with suitable means to facilitate its connection with a metallic conduit. This may be done in any desired manner. In the method shown in Fig. l the tube is provided with an enlarged collar [6 and with the securing flange [1. A similar flange 18 is welded or otherwise attached to the metallic conduit I9. The flange [8 may thus readily be brought into tight contact with the collar it by means of the bolts 20. Any suitable gasket material may be interposed between the flange l8 and the collar It to insure a gas-tight joint.

The metallic tube 19 may comprise a portion of an ordinary rigid metallic tubing or pipe system. In order to compensate for the linear expansion of tube section [0, which is subjected to the high temperatures, it is desirable to insert a short length of flexible metallic tubing, such as section 2|, between tubes H] and I9. Such a flexible tubing provides, in effect, an expansion joint absorbing the differences in linear expansion during the operation. In lieu of the flexible tubing 2| any other similarly functioning connection may be employed.

It will be particularly observed that the tubes are supported wholly on the floor of the furnace through the medium of the lower return bends while, on the other hand, the upper return bends are spaced an appreciable distance from the roof of the furnace, as shown at 22. Hence, in this type of construction the weight of the tubes is taken as a vertical compression load and the tubes are free to expand and contract in a vertical direction with changes of temperature in the furnace.

As previously pointed out, a novel type of joint is established between the upper return bends and the tubes. This is shown in more detail in Fig. 2. As there shown, the return bends 6 and l are disposed so that the horizontal axis of each is parallel to the floor while the tubes 5 are disposed vertically with their axis normal to the horizontal axis of the return bends. The upper ends of the tubes 5 are specially conformed. As will be seen, the hearing or contact surface between the upper end of the tubes 5 and the upper return bend 6 is curvilinear. Preferably also, the section of tube 5 adjacent the contact or bearing surface is thickened, as shown at 23. This not only increases the strength of the tubes at this section but also provides increased hearing or contact area. It will be observed that the abutment established between the upper end of the tube 5 and the return bend 6 thus co s i ut in effect, a type of ball and socket bearing surface, the purpose of which will presently appear. The lower ends of the tubes 5, as shown, fit into angular rather than curvilinear sockets in the lower return bends T. The tubes 5 are joined to the upper return bend 6 and to the lower return bend I by means of a suitable cement.

In the past, such joints could be made gastight and remain gas-tight if the tubular system was not permitted to rise a great deal in temperature. However, in earlier constructions as the system was brought up to the desired high temperature, expansion of the several units took place. As will be observed, the tubes expand upwardly since the bottom return bends to which the tubes are connected rest on the furnace floor. Since the tubes and return bends are of different shape and cross-sectional dimension the extent of both linear and cubical expansion of the two is different. At the high temperatures the upper return bends expand in all directions while the lower return bends expand in all directions except downwardly, being restrained from such movement by the furnace floor. Expansion of the return bends in a vertical direction manifestly does not tend to change the position of the tubes relative to the return bends. I-Iowever, expansion of the return bends in a direction parallel to their horizontal axis does modify or change the vertical position of the tubes and it is this movement which has been one of the important factors in the unsatisfactory operation of prior refractory tubular systems.

The effect of such a displacement of the tubes 5 from a vertical position can be more readily appreciated by a reference to Fig. 2. It will be observed that each upper return bend 6A and 6B is connected to two tubes, namely, 5A and 5B. Similarly, each lower return bend 1A and 7B is connected to two tubes 5A and 513. With increase in temperature that portion of the upper return bend 6A to which the tube 5A is connected expands laterally in the direction indicated by the arrow A while simultaneously the portion of such upper return bend to which the tube 5B is connected expands laterally in the opposite direction indicated by the arrow B. At the same time the section of the lower return bend 1A to which tube 5A is connected expands in the lateral direction indicated by the lower arrow B. Since the tube is constrained to move with the return bend it is apparent that the tube 5A, shown on the left hand side of Fig. 2, for example, tends to assume a position the axis of which is shown by the dotted line 24. It will be appreciated at this point that the slope of line 24 is exaggerated to more pointedly illustrate this displacement of the tube and not as attempting to show its precise position. Similarly, the tube 5B, due to lateral expansion of the return bends, will tend to assume a position the horizontal axis of which is indicated by the dotted line 25. It is thus apparent that while tubes 5A and 513 may be vertical and parallel when cold yet as the temperature is increased they tend to converge at the bottom and diverge at the top. It is obvious that if joints 8 and 9 are rigid a fracture would soon occur either in the tube, or in the joint, or both, to allow the tube to assume such non-vertical position at the higher temperature. Now, according to the present invention this result is avoided by establishing or providing flexible joints between the tubes and the upper return bends on the one hand, and the lower return bend on the other.

t rm of a powder.

; displacement.

AS previously 1 explained, .a curvilinear or ball and socket type of joint is .estahlishedbetwech the upper return bends .and the tubes, .With this type of construction lateral expansion of the upper-return bendfi, as viewed in 'Fig,"2, tends toforce such return'bend to more in rela tion toithe tube instead of, as in priorconstruc tions, constraining the tube to takeup this total expansion. Inasmuch as the joint between the upper return bend and the tube is as ctor ofa .spherethe duality ofthe joint, he thereutinuous. contact between the abutting snriaceis not impaired'by this-relative movement.

As noted previously, the curv l near contact .sur-Iaceis not used ,as a joint between thelower returnbends andthe-lo-wer ends of the tube. This isbecause the coil orrtubule sy tem see Wholemustbe substantially r id- ;Ithas be fen d fr m exper ence that the lower ti -int 9 may be termed, as howh, i. .e-,-as-asimp eahsu ar join properly emented. As ias been inunrat d previously, th reem nt l i/win the joints is of p me importa ce is st l h-ins has-been found ha h s g ght fit may b secured by utilizing a cement whichis relatively igid when cold but becomes softened or plasticized at high temperaturessoas toperlnitth t rela ve esr ecf movemen of th tu e that he upper curvilinear bear-ingsurface had not ac eommodat t ha been found hat in li u of utilizing cement that becomes p as ic a h g temperatures the cement may be applied in the It s u d be o serv d that the thicknessor depth oi the plas i sir-powder iointmust e great i ugh t with and th pressure of the gas in the tubular system. In this connection it should be noted thatat. the

relativelyc ol -p r n i h ystem, ad-

jacent the inlet line 293. the pressure is highest and care must be ex cised in insur ng t proper depth of plastic at the joints in this area. .Itis appar nt that withinthe broad s pe o the invention anum e of ra ified. spe ficaliy different as stations of the tubes-t and thereturn bendsb and 7 may e employed. An

xample of such. a modified form of continu u coii is shown diagrammatically 13. As there shown, the vertically positioned pairsuof tuieesaififiere disposed in an offset or staggered relationship. The upper return bends Gil are positioned in a plane such that the major horizontal axis is normal to the major horizontal axis of the lower return bendii}. In this type of continuous coil the expansion of the return bends, in effect, imparts a rotational motion to the tubes and commensurately reduces angular As in the case of the structure .shown'in 1 and .2, the employmentof a curvilinear contact surface between the upper ends of the tubes and the upper return bends, together with the employment of plastic or powder cement for the lower joint minimizes or obviates the "effect oi. the expansion of the return berids.

As mentioned previously, the continuous coil formed by the described association of tubular elements and return bends may be connected in circuit to units located exteriorly of the furnace in a number of ways. In the structure shown in Fig. 1 the inlet pipe l0, if a separate element, is connected to the L l2 through an angular joint i4, similar to joint 9. It will be understood that a ball and socket joint at this particular location All] would be undesirable beeau ei ther ll n lack of rigidity of the tubularsystem. it as been "found that an insert joint at is not as effective in retai ing a pressure-t h id a is the Joint 9. This isprebab du o th eet that the joi t .9 tends to remain ti ht ue o the wei ht of the supe posed str ctu name y. the weight of the ube 5 and the associated upp r turn b nd. H wever, mpr v d Jo n s a this section ofv the structure may be produced by form the tube in an l- 2 i on P e ethus completely eliminatingthe joint I4, There are a number of other methods of insuring a gasti-ght fit at this section of the apparatus. For example, the L .l 2 ay be repl c d w th a r u n bend and the inlet line or pipe is may bentted verti al yin such re urn end inthe s m ma ner as the tubesthen extended vertically through the roof or": th u na e. Th e d o the P pe I 0 ositioned exter ly of th ace m th n be joined or connected o a m tal ic tub 9 n the manner own n E' e-..1- gain, i de i the .1- l2 may be el m na ed nd th fi st tube 5C Fi .1) may be e t nded do n ro gh t e .floor of the furnace and ouneetede er e y of h furnace with-ametal ie co d E9 in a manner equivalent to that shown-in Fig. 1.

;It is, apparent that the modified types of con.- nection, of their-11st line or conduit ill to the first tube are equally applicable to the connection be.- tween the last tu Qf he seri s and th outle r zd se a seil ne i, .It is a ai to e noted, a this po nt, tha he pre u er d a the jo n is somewh t low tha t a aga ns Join 14 and this fact should be recalled forming the cemented j i ts,

Thee iicaey of utili n -the Prin iples of th invent on willemore readi y ap e iated from a .e. nsidera o actual o era s n which eon inu u -rtubular co l tru ure fabric t cording to prisr methods were directly compared with similar structures embodying the novel ipr' eirles th nventi Afurnace was coned in accordance with Fig, l with the BX- fception that 'thej-oints 5, 9 and it were made ri id.- The t be and eturn bends were st et d of sil con carb e o e y bondedr wa p ehea d in a iur a fi ed wi h ypi a metallic heating tubes and up to a temperature of .tl60.0 Th s a r w sth n ntroduce into th h gh temper tur efractory u nac whe e theltemneratu e ra s d t Wh le, ashoted, the refractory furnace was brought up :to the operating temperature very slowly, in .con-

formity with good operating practice, serious .leaksdeve oped fter app ox mate y ix w s of operation and became progressively worse with c ntinued use of the u na e. After an eight weeksmer od e t pe a ion t e furna w gradual-iv co led a d the leaks repai ed y apply n .a ceme t wh c wasbas allythe same material as thatei wh ch the tubes and eturn bend w re abr. ea ed.- This epair pe m ted a a d tional weeks. oi ope ati n a er whi h t meth l ak re urred to ade r e w h m te i y impa re the operation of th urnace. have been repa ed again a t r su h operation The furnace .could 7 leaked from both the impaired joints and the cracks in the tubes.

A furnace was constructed embodying the principles of the invention to establish a direct comparison with older structures. Ball and socket joints, as indicated in Fig. 2, were used between the upper end of the tubes and the upper return bends while the lower angular oints 9 were cemented using a silicon carbide base cement to a depth of 1 inches. The cement used throughout the furnace was essentially the same differing only in a temperature at which it became plastic. As will be understood the particular cement used in any part of the furnace is dictated or established by the temperature of the air inside the tubes at the particular point where the cement is employed. The furnace embodying the novel features of the invention was brought on stream in the manner described and was operated for a period of three months without any perceptible damage to any of the tubes, return bends or Ls and with but minor damage to any of the joints excepting joint 14.

The furnace was then modified in accordance with principles heretofore discussed, namely, by removing the L I2, substituting a return bend therefore and extending tube It! vertically through the roof 3 of the furnace. It was found that in this structure the tubes, return bends and L IS were intact and undamaged after a total period of operation of nine months while the blow holes and porosities in the joints were so small and so minor in extent that the loss of air due to leaks through the joints was not practically measurable.

While preferred modifications of the invention have been described it will be understood that these are given to illustrate the novel principles involved and not as limiting the invention to the particular design or arrangement of the several units of the coil structure shown.

I claim:

1. An apparatus for heating fluids comprising a furnace, a continuous coil within the furnace through which fluids to be heated are passed, the coil including a series of vertically positioned, refractory, ceramic tubes and a series of upper and lower refractory, ceramic return bends of different shape and cross sectional dimensions than the tubes and connected with the tubes to form a continuous coil, the coil being characterized by a spherically concave-convex joint between the upper return bends and the tubes and by an angular joint between the lower return bends and the tubes.

2. An apparatus for heating fluids comprising a furnace, a continuous coil within the furnace through which fluids to be heated are passed, the coil including a series of vertically positioned, refractory, ceramic tubes and a series of upper and lower refractory, ceramic return bends of different shapes and cross sectional dimensions than the tubes and connected with the tubes to form a continuous coil, the coil being characterized by a spherically concave-convex joint between the upper return bends and the tubes and by an angular joint between the lower return bends and the tubes, said joints being sealed with a refractory cement.

3. An apparatus for heating fluids comprising a furnace, a continuous coil within the furnace through which fluids to be heated are passed, the coil including a series of vertically positioned, refractory, ceramic tubes and a series of upper and lower refractory, ceramic return bends of different shape and cross sectional dimensions than the tubes and connected with the tubes to form a continuous coil, the coil being characterized by a spherically concave-convex joint between the upper return bends and the tubes and by an angular joint between the lower return bends and the tubes, said joints being sealed with a refractory cement which is plastic at the operating temperature of the furnace.

4. An apparatus for heating fluids comprising a furnace, a continuous coil within the furnace through which fluids to be heated are passed, the coil including a series of vertically positioned, refractory, ceramic tubes and a series of upper and lower refractory, ceramic return bends of different shape and cross sectional dimensions than the tubes and connected with the tubes to form a continuous coil, the coil being characterized by a spherically concave-convex joint between the upper return bends and the tubes and by an angular joint between the lower return bends and the tubes, said joints being sealed with a refractory cement of the same general composition as the tubes and return bends and which is plastic at the operating temperature of the furnace.

5. An apparatus for heating fluids comprising a furnace, a continuous coil within the furnace through which fluids to be heated are passed, the coil including a series of refractory, ceramic lower return bends mounted directly on the floor of the furnace, a series of upper refractory, ceramic return bends spaced from the roof of the furnace, a series of vertically positioned, refractory, ceramic tubes connecting the upper and lower return bends, the coil being characterized by a spherically concave-convex joint between the upper return bends and the tubes, means including an expansion joint to connect one end of the coil to an inlet line exteriorly of the furnace and means to connect an outlet line to the other end of the coil.

DAVID H. GREENE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Num er Name Date 457,589 De Navarro Aug. 11, 1891 1,711,821 Abbott May 7, 1929 2,472,497 Stookey June 7, 1949 FOREIGN PATENTS Number Country Date 47,524 Denmark July 10, 1933 376,959 Germany June 8, 1923 

